What’s FREE SPAN?

In offshore pipeline projects , free span is a condition when a pipeline is not laid correctly on seabed (see below pic). This condition can be happened because of some reason such uneven seabed, pipeline crossing, tie-in to subsea structures, sleeper, soil scouring, sand waves, etc. Free span condition causes problems in both static and dynamic aspects. If the free span length is too long, the pipe will be over-stressed by the weight of the pipe plus its contents. The drag force due to near-bottom current also contributes to the static load. To mitigate the static span problem, mid-span supports, such as grout bags or sand-cement bags can be used.
installing grout bags under pipeline and filling it with mixed high sulfate resistance cement (type V) and sea water is normal method for correction of free span.